Semiconductor processing typically requires several stages of surface etching and layer depositing to form circuits thereon. One device used to perform such etching and depositing is known as a parallel plate reactor. The parallel plate reactor resembles a typical bath-type showerhead in that it comprises a flat circular metallic disc with holes passing therethrough. Radicals are formed between the plates of the parallel plate reactor and directed through the holes therein onto a wafer below.
While the parallel plate reactor is an effective device for processing a wafer, the excitation of a gas creates electrons and ultraviolet light which then bombards the wafer, along with the plasma. Electrons and ultraviolet light generally have a negative effect on the process of depositing or etching the wafer and are therefore undesirable. The bombardment of the wafer by electrons reduces the processing selectivity, i.e., the ability of the radicals to remove or deposit only the desired materials is reduced. A parallel plate reactor typically produces selectivities in the range of 30 or 40 to 1.
Another device, created to reduce the bombarding of the wafer with electrons, is a microwave-induced plasma remote processor. With a remote processor, a metallic box is placed around a quartz tube and microwaves are generated to create a reactive species. A gas is pumped into the quartz tube and excited into a plasma state therein. Due to the shape of the quartz tube, many of the electrons are prevented from escaping the tube to bombard the wafer.
Unfortunately, most of the gases used to process a semiconductor wafer react with the quartz material from which the quartz tube is made. Thus, the excitation of the gas into radicals causes an increased deterioration of the quartz material by removing particles thereof which are carried with the radicals to be deposited onto the wafer. Any foreign particles such as quartz that are deposited on the wafer tend to mask the wafer during deposition or etching, which can cause the circuit being built to be destroyed.
Thus, a greater selectivity (300 to 1) is reached by the use of the remote processor, but due to the deposition of quartz particles, the benefit of increased selectivity is wasted. Thus, there is a need for a method and apparatus that has enhanced selectivity without depositing contaminants onto the wafer.